1. Field of the Invention
This invention relates to a thermoplastic benzophenone polyester, consisting essentially of the moieties of 2,2-bis(4'-hydroxyphenyl)propane and 4,4'-benzophenonedicarboxylic acid, a process for its preparation, and a shaped article prepared from the polyester having an impact strength of at least about 2 ft.lbs./in. of notch as measured by the Izod impact test, ASTM D-256-56.
2. Brief Discussion of the Prior Art
Thermoplastic aromatic polymers are well known in the art as being useful for making shaped and molded articles. Aromatic polyesters are especially desirable for this purpose since shaped articles derived therefrom tend to exhibit low moisture absorption, high heat deflection temperature, and high impact strength, all of which are desirable characteristics of such articles in many industrial applications. Examples of such applications are in the manufacture of industrial safety glass and safety housing units for plant machinery. Shaped articles made for these purposes should generally possess an impact strength of at least about 2 ft.lbs./in. of notch as measured by the Izod impact test, ASTM D-256-56.
A benzophenone polyester derived from 2,2-bis(4'-hydroxyphenyl)propane (bisphenol A) and 4,4'-benzophenonedicarboxylic acid chloride is known in the art and is disclosed in U.S. Pat. No. 3,028,364 (Conix, et al., 1962) and Industrial and Engineering Chemistry, Volume 51(2), pp 147-150 (1959) by Andre Conix. The above-identified patent discloses a general method for preparing fully aromatic polyesters by interfacial condensation polymerization, wherein an aromatic diacid chloride, dissolved in a chlorinated hydrocarbon solvent, is mixed with an aqueous solution of an alkali metal salt of a bisphenol, thereby forming an aromatic polyester which dissolves during its formation in the chlorinated hydrocarbon solvent. The above-identified journal article, by the same author, describes specifically an aromatic polyester made by this procedure from 4,4'-benzophenonedicarboxylic acid and bisphenol A having an intrinsic viscosity of 0.72 deciliters/gram.
These references also teach that, in order to obtain a high molecular weight polyester, as indicated by high intrinsic viscosity, the chlorinated hydrocarbon solvent should be a solvent for the polyester so that the polyester is obtained in solution form. While it is known that the impact strength of a polyester may sometimes increase with its molecular weight, this effect is not generally predictable.
Shaped articles made from the 4,4'-benzophenonedicarboxylic acid/bisphenol A polyester, produced by the prior art process, do not exhibit impact strengths of at least about 2 ft.lbs./in. of notch, as measured by ASTM D-256-56.